Catalysts for purifying exhaust gas

ABSTRACT

Exhaust gas purifying catalysts characterized in that alloys comprising 0.1-40% of Cu and the balance of Ni and/or Fe by weight as fundamental components are shaped as desired and are activated, at least partially, by providing their surfaces with oxidized enriched Cu layers thicker than 10 Beta in the oxidization atmosphere or by partially reducing the oxidized layers with hydrogen gas at high temperature.

United States Patent Niimi et a1.

CATALYSTS FOR PURIFYING EXHAUST GAS Inventors:

Assignee:

Filed:

Appl. No.:

' Itaru Niimi, Nagoya; Yasuhisa Kaneko, Toyota; Akiyoshi Morita, Toyota;Yasuo Nemoto, Toyota; Mitsuyoshi Sato, Toyota, all of Japan ToyotaJidosha Kogyo Kabushiki Kaisha, Japan Feb. 12, 1973 US. Cl. Int. CL

......... 252/470; 252/474; 423/213.5 BOIJ 23/86; B01J 23/72 Field ofSearch 252/470, 474; 423/2132,

References Cited UNITED STATES PATENTS Hodge 252/470 X Dec. 23, 19753,206,414 9/1965 Gunther 252/474 3,565,574 2/1971 Kearby et a1. 252/474x 3,699,683 10/1972 Tourtellotte et a] 423/2132 x 3,718,733 2/1973061111 423/2132 3,773,894 11/1973 Bernstein et a1. 252/474 X FOREIGNPATENTS 0R APPLICATIONS 354,692 2/1930 United Kingdom 423/2132 PrimaryExaminer-W. J. Shine Attorney, Agent, or Firm-Connolly and Hutz [5 7]ABSTRACT Exhaust gas purifying catalysts characterized in that alloyscomprising 01-40% of Cu and the balance of Ni and/or Fe by weight asfundamental components are shaped as desired and are activated, at leastpartially, by providing their surfaces with oxidized enriched Cu layersthicker than 10 1 in the oxidization atmosphere or by partially reducingthe oxidized layers with hydrogen gas at high temperature.

3 Claims, 16 Drawing Figures US. Patent Dec. 23, 1975 Sheet 2 of43,928,241

After annealing Casted as is Fe-2. 8%Ni-O.5%Cu

(Specimen No. 1)

casted as is After annealing Fe-Q-SZCu (Specimen No. 16)

Ni-24.0ZCu (Specimen No. 18)

US. Patent Dec. 23, 1975 Sheet 3 of4 3,928,241

c d as i After annealing Fe32.0%Ni-l7.7%Cu-3.9ZA1 X 200 (Specimen No.27)

casted u 1.

];5% C -1. 6181 (Specimen No. 22)

casted as is Fe-28-9ZCu-33.0ZCO gg s (Specimen N0. 33)

US. Patent Dec. 23, 1975 Sheet4 0f4 3,928,241

X 300 Fe-52.0ZNi-26. 4ZCu (Oxidized layer thickness 0.6mm

Oxidized at 900C. for 24 hours) X 1000 Surface of alloy without oxidizedlayer X 1000 X 3000 Fe-52.0ZNi-26. 4ZCu Fe52.0ZNi-26. rZCu (Oxidizedlayer thickness 0.6mm (Oxidized layer thickness 0.6mm

Oxidized at 900C. for 24 hours) Oxidized at 900C for 24 hours) CATALYSTSFOR PURIFYING EXHAUST GAS BACKGROUND OF THE INVENTION The presentinvention relates to a catalyst for purifying exhaust gas.

Conventional industrial catalysts suitable for purifying exhaust gas areagents which are generally made by allowing carriers such as alumina tocarry noble metals such as Pt or Pd or carry or mix with oxides of Ni,Cu or Cr. But these are significantly disadvantageous in that catalyticagents comprising noble metals such as Pt or Pd are expensive, theirresources are insufficiently available, inferiority in heat resistanceand durability, and unsuitability for quantity production due todifficult manufacturing methods. Various other alloy system catalystsare known in addition to catalysts as mentioned above, but these do notdemonstrate their effects if temperature is not high.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to provide a unique catalyst for purifying exhaust gas whichavoids the drawbacks of the prior art and which functions in a highlybeneficial and economical manher.

The present invention relates to exhaust gas purifying catalysts havingcharacteristics for removing harmful nitrogen oxide (NOx) componentscontained in exhaust gases, particularly those from internal combustionengines, by reduction, and is characterized in that alloys comprising 0140% of Cu and the balance of Ni and/or Fe by weightare provided withenriched Cu layers on their surface portions, or further, the oxidizedlayers are partially activated. I

BRIEF DESCRIPTION OF THE DRAWINGS Novel features and advantages of thepresent invention in addition to those mentioned above will becomeapparent to those skilled in the art from a reading of the followingdetailed description in conjunction with the accompanying drawingswherein similar reference characters refer to similar parts and inwhich:

FIG. 1 is a diagram of alloy composition ranges of the I catalystsaccording to the present invention;

FIG. 2 is a graph diagram showing therelationship between NO and COpurification rates and catalyst bed temperatures;

FIG. 3 through 8 are microscopic photographs of typical alloys andcatalysts obtained in embodying Examples I through 6 according to thepresent invention;

FIG. 9 is a photograph made by a scanning-type electronic microscopeillustrating the state of an alloy surface in the case where an oxidizedlayer is absent from the surface; and

FIG. 10 comprises photographs made by a scanningtype electronicmicroscope illustrating the state of an alloy surface in the case wherean oxidized layer thicker than 10g. is present.

DETAILED DESCRIPTION OF TI-IEINVENTION The present invention is intendedto provide catalysts for reducingand removingNOx contained'in exhaustgas discharged from internal combustion engines. The

dance with a wide range of applications. Compositions and manufacturingof exhaust gas purifying catalysts according to the presentinvention'are described below.

Asfor compositions of alloys according to the present invention,catalysts of this invention comprise a binary Fe-Cu or Ni-Cu or aternary Fe-Ni-Cu system alloy (hereinafter referred to as this systemsalloy) always containing less than 99.9% of Fe and Ni and the balance ofCu.

In this'case, it is possible to reduce contents of Fe and Ni as desiredand instead, to add elements other than Fe, Ni and Cu less than 10% byweight.

The type of elements to be added is not particularly restricted, butsince C0 and Cr efficiently achieve the catalytic effect, addition ofthose elements up to 40% by weight is acceptable. Co demonstrates theeffect similar to that of Cu. Of course, nonmetallic elements such as Cand Si which are contained in usual alloys also may be added.

A composition range of this systems alloy for the catalysts according tothe present invention is given in FIG. 1. A portion rectangularlysurrounded by ABCD is a standard composition range. Even in case otheradditive elements are contained, if the composition rate is within adiagonallylined range, that composition is acceptable. In thepresentinvention, this system's alloy within the above composition rangeis obtained by the conventional method and is shaped in workableplasticity types such as a sheet, bar, pipe, line or alloy powder,casting materials, etc., according to alloy compositions andapplications for use as catalysts.

It is an essential factor in producing alloy catalysts to place oxidizedlayers thicker than 10p. over the alloys. The catalysts according to thepresent invention, can function satisfactory with an oxidized layeronly, but those are further improved by reducing the oxidized layersformed on alloys. Descriptions as to examples embodying the presentinvention are given below. In each of these examples only one-half ofthe specimen is reduced after oxidation to thereby provide a comparisonbetween oxidation alone and reduction after oxidation.

EXAMPLE 1 After melting Fe-Ni-Cu ternary alloys with variouscompositions as given in Table 1 at l600C. by using a Tammann furnace, acasting was made in a stainless steel (SUS 27) mold coated with asufficient thickness of graphite. After casting, casted cylindricalbars'obtained were machined tomake cuttings and were subjected tooxidization treatment in a high temperature atmosphere at 1000C. for sixhours to obtain catalyst cuttings.

By producing the cuttings as described above, an apparent surface areaper unit weight becomes wider. The dimensions of the cuttings vary withthe material, but those within the range of 0.1 0.5mm in thickness,2mm-20mm in length and lmm-3mm in width are desirable. The term Cuttingsin this Example and hereinafter, represents granularity almost withinthe above range.

Further, half of the catalyst (after oxidization) obtained as above, wasreduced at 800C. in hydrogen gas for two hours. Alloy compositions andpurification rates of the catalyst obtained by the above process aregiven in Table 1. Chemical components given in the Table show alloycompositions after casting and the 3 purification rates are results ofthe test using 10ml of the catalyst. The above explanations are commonin Table 2 and succeeding tables.

Table 1 Compositions and purification rates of Fe-Ni-Cu system allo Thecatalysts apparent surface area of 10ml is desped- Chemical componentNpyurjficmion mite pendent on the catalyst components, but is almost 1 pi g i y ft within 100 l000cm Unless otherwise specified,- the Cu Ni Fe:f; surface area 15 identical to that in Example 1.

2 0.8 ba EXAMPLE 2 3 0.9 8.9 ba:

The binary alloy with a COmPOSIUOIIOOf Fe and Cu as 5 26 m bal 195 64.3given in Table 2 was casted at 1650 C. in the same 6 4,4 50,8 bal 51.386.2 metal mold as in Example 1 after being melted in a high 3-; 2:: 2-323-? frequency f q 9 6:4 17:5 bal 313 800 Casted cylindrical barsobtained were machined to 1? g-g 2% make cuttings and the cuttings weresubjected to oxldi- 12 5 4 zation treatment in an atmosphere at 1100 C.for three 13 10.9 42.1 bal 0 72.1 hours to obtain catalysts. Also, halfof the cuttings were 14 223 bal 0 0 15 26.4 52.0 bal 0 78.5 reduced mhydrogen gas at 800 C. for two hours to obtain catalysts.

' 20 EXAMPLE 3 Table 2 A sheet-type catalyst was obtained by subjectingCompositions and purification rates of 0.5mm thickness of an Ni-Cu alloyto atmospheric System alloys N0 oxldlzatlon 800C l and 1 for Speci-Chemical Oxidation/Reduction purification 24, 12, 6 and 3 hours,respectively. men component rate This sheet-type catalyst had beenshaped cylindri- Fe cally at 0.5mm in thickness, 2.5mm in width and 15mm16 2 5 b l 0 6 8 an n in length. A half: of the catalyst was Sub ectedto hydroa f f 2 gen gas reduction at 800C. for 2 hours. Apparentoxidization 70.0 surface area of a 10ml catalyst obtained by the above17 bal process was approximately 100cm.

EXAMPLE 4 Fe-Ni-Cu alloy comprising other additive elements as Table 3givenin Table 4 was made into cuttings and subjected Treatmentconditions and purification to high temperature atmospheric oxidizationat S Ch I I 6 9 7 yg C0 ecl- 8111108 Xl 1Z3 1011 1000C. for 6 hours, anda half was Subjec to y glen component Reduction purificationpurification gen gas reduction at 800C. for 2 hours. No. c N rate rateEXAMPLE 5 40 80.0%.

Fe-Cu binary alloy comprising other additive eleg 'g'fi g: ments asgiven in Table 5 was made into cuttings and after subjected to hightemperature atmospheric oxidization 6323 at 1 100C. for three hours, anda half was subjected to oxidizatjon 763 hydrogen gas reduction at 800C.for 2 hours. Redactlon a er 18 24 66 oxidization 54.3 46.0 EXAMPLE 61990,?

Ni-Cu alloy comprising other additive elements as 0 0 eductlon given 111Table 6 was formed into a 1.0mm thick sheet after and subjected to hightemperature atmospheric oxidigggg 531 zation at 900C. for twelve hoursto obtain a sheet-type oxidimion 0 1 catalyst, and a half was sub ectedto hydrogen gas re- Redpction 0 8 181' duction at 800 C. for 2 hours.The sheet with dimenoxidizafion 62.0 482 810118 of 1.0mm X 2.5mm X 15mm,the same as m Example 3, was cylindrically formed. Apparent surface areaof 10ml catalyst was approximately cm Table 4 Fe-Ni-Cu additive elementsystem alloys and purification rates Chemical component NO purificationrate Oxidization/Reduction Specimen Oxidization Reduction No. after CuNi Fe Others oxidization 19 8.8 30.4 bal C-l. Not 75.0

Si-2.2 measured Co-2l.4 20 9.8 18.4 bal C-2.1 72.1

Si-2.3 21 11.6 39.8 bal C-l.6 80.9

Table 4-continued Fe-Ni-Cu additive element system alloys andpurification rates Chemical component N purification rateOxidization/Reduction Specimen Oxidization Reduction No. after Cu Ni FeOthers oxidization Si-2.l 22 17.7 47.6 bal C-l.5 72.0

Si-l.6 23 17.7 32.0 bal Al-3.9 3.7 74.1 24 18.9 47.4 bal C1 .1 Not 72.0

Si- 1 .6 measured 25 27.9 17.3 bal Si-'4.3 75.3 26 24.3 39.1 bal ICe-4.l 1.8 Not measured 27 29.7 3.7 bal Al-2.8 2.8 77.7 28 30.1 8.9 balSi-3.l 0 70.4

using X-ray diffraction after subjecting same to reduc- Table tiontreatment.

Fe-Cu additive element system alloys and purification rate Chemicalcomponent NO purification rate Reasons for restricting each componentelement in this systems alloy, which is a basis for the catalystaccording to this invention, and its effect are presented below.

As for Cu, when this system s alloy has been oxidized and subsequentlyreduced to impart a catalyst effect, CuO* is formed on the alloysurface, and CuO* being diffused into FeO* and NiO* is presumed to playa significant role for catalytic effect.

CuO* herein represents oxidized Cu, but since the state of achieving theoptimum catalytic effect is unknown and content of oxygen can not bedetermined, representation is made by 0*.

Catalytic activity is deemed to become present when 0* in oxides isalmost nil. FeO* and NiO* denote the same as in CuO*.

When the surface of alloys subjected to oxidization treatment at hightemperature was examined by utilizing X-ray diffraction to certify theabove matters, compositions were proven as follows.

CuO* CuO FeO* Fe O (Hematite) NiO* NiO Moreover, the followingcompositions were also clarified when the surface of the alloy wasexamined by However, it can not be concluded that all of them are in thesame state as mentionedabove.

The reason for restricting the Cu content is that when Cu exceeds 40% orbecomes less than 0.1% by weight, diffusion of CuO* into NiO* and FeO*becomes dense and coarse respectively, and either case adversely affectsthe catalytic effect. In case Cu is excessive, it separates and depositsin the alloy provided that it does not form a solid solution orintermetallic compound.

This problem is caused due to the presence of Fe as seen from the Fe-Cubinary state diagram given in FIG. 1, and deposited Cu does not havecatalytic effect.

Intermetallic compounds are difficult to oxidize, and even if oxidized,those compounds do not form oxidized layers having catalytic effect.Therefore, although Cu is contained therein, it adversely affects thecatalytic effect. The more this systems alloy contains solid solutionFe-Ni-Cu or Fe-Cu, the greater the catalytic effect becomes. Now, as forNi and Fe, it is felt that Ni and Fe act to promote the catalytic effectrather than to provide the direct reduction effect to NOx, that is, adispersed state of CuO* is thereby made effective and the effect ofadsorbing molecules such as CO and H useful for reduction of NO isexcellent.

Meanwhile, Ni is effective for expanding a solid solution limit of Cuinto Fe, which can be presumed from the binary state diagram of Ni-Cuand Fe-Ni given in FIG. 1. Coexistence and independent existence of Niand Fe are acceptable.

1f additive elements satisfy the following conditions when added to thissystems alloys of Fe-Ni-Cu, Fe-Cu or Ni-Cu, the catalytic effect willnot be reduced much, that is;

1. Permeation into solid solution.

2. Non-production of intermetallic compound with 3. Non-deposition of Cudue to presence of additive elements.

Moreover, if additive elements less than 10% by weight satisfy the aboveconditions, the catalytic effect will be obtained. The less the degreeof satisfying the conditions becomes, the lower the catalytic effectbecomes, but as long as additive elements do not exceed 10% by weight,the catalytic effect will be substantially maintained.

Also, even if graphite is crystallized in the alloy structure by addingcarbon or silicon, the catalytic effect will not be adversely effected.As for Co, it acts similarly to Cu as described previously and it isunnecessary to restrict the content of Co, but the upper limit isdetermined in relation to the coexistence with Fe and Ni. As for Cr, itdoes not considerably lower the catalytic effect and the content maywidely be restricted. However, the content of Cr over 40% is undesirablefrom a standpoint of melting and subsequent workability.

In addition to the description as to component elements, microscopicphotographs of casted and annealed structures of component elementsgiven in Examples 1 through 6 are presented in FIGS. 3 through 8 inorder to clarify the effect of each component. Annealed structures arethose which are annealed by furnace cooling after heating at l000C. for6 hours.

Then, actions of oxidized layers and reduced layers which are essentialfor obtaining optimum catalytic effect are described. Oxidized layersare formed by oxidizing in atmospheric conditions. Since thicknesses ofoxidized layers vary with alloy compositions, surface condition,oxidizing temperature, and period of oxidizing time, treatmentconditions can not be formulated, but desired thickness is obtainable byselecting conditions within temperatures ranging from 700 to 1 100C. andtime periods ranging from 1/2 hour to 24 hours or temperatures rangingfrom 800 to 1300C and time periods ranging from 3 to 24 hours.

The thickness of oxidized layers are required to be at least 10p. and athickness above 10p. is unlimitedly permissible, to the extreme of up tothe center portion of the alloys.

On the contrary, as the thickness becomes less than 10 1., the catalyticeffect is remarkably deteriorated and at last becomes unobtainable ifthe temperature is above 700C. This is considerably due to the effect ofCuO*, NiO*, FeO*, etc., against the catalytic activity as previouslydescribed in the compositions. Also, the oxidized layer with a thicknessof at least 10p. is necessary to provide oxidized layers withcorrugation and to increase the surface area as will be described later.As a result of examining composition variations of oxidized layers byusing an X-ray micro-analyzer, the following matters became clear, thatis enriched Fe and Cu layers are formed at the top surface, andmoreover, the enriched Cu layer is placed close to the surface more thanthe enriched Fe layer. This tendency becomes further obvious byproviding a reduction treatment and the enriched Cu layer exists at thevery top surface.

An enriched Ni layer is also formed at the portion near the surface, butslightly lower than the enriched Fe and Cu layers, and after subsequentreduction treatment, in the same position as that of the enriched Felayer or slightly close to the surface. The enriched Cu layer formednear the top surface exists independent from other additive elements. Codisplays an enriched state similar to that of Cu.

In case the oxidized layer is thinner than 10 1., the enriched oxidizedlayer, as described above, can not be formed. On the other hand, as theoxidized layer becomes thicker, the above tendency becomes considerablymore, that is, Cu enriches in the surface and diffuses into Ni and Fe.This is an advantageous condition for catalytic effect. In Examples 1-6,since the thickness of all oxidized layers were made in 0.5 1.0mm,

the above condition was satisfied. As a result of observing oxidizedlayer surfaces by a scanning-type microscope, it became clearer that theoxidized layer surfaces were corrugated and porous, that this tendencybecame extreme when the oxidized layer thickness was less than 10a, andfurther, that this tendency became' obvious when the oxidized layer wassubjected to a subsequent reduction treatment.

Thus, an oxidized layer thinner than 10p. apparently lowers itscatalytic effect, as seen from the above surface observation results.This tendency is shown in FIGS. 9 and 10. FIG. 9 shows the surface whenthe oxidized layer is insufficiently formed and corrugation and porosityare not seen therein, but are apparent in FIG. 8 which shows the stateof a sufficiently oxidized layer.

As described in the Examples, the reduction treatment of an oxidizedlayer is the processing in hydrogen gas and the treatment condition isdetermined within the treatment period of time ranging from 24 hours inaccordance with the state of the subject oxidized layer, and at least,partial treatment is acceptable.

Thereafter, the test results on catalytic effects by catalysts accordingto the present invention are presented.

TEST EXAMPLE 1 The purification rate as to NO was measured under thefollowing conditions in order to certify the effect of each catalystobtained in the embodying Examples l6.

Devices employed:

Test gas:

Gas flow rate: Amount of catalyst: Type of catalyst:

S.V. (Space Velocity):

Catalyst bed temperature: Catalyst surface area:

2. Results The results are as given in Tables 1 through 6. Each resultshows an excellent NO purification rate. Certain catalysts do notachieve sufficient purification ability with their oxidized layers only,but it has been known that the effect can be improved by providing samewith reduction treatment. As a result of testing with alloy systemsother than this system's alloy under the same conditions, neither onedemonstrated a suffficient NO purification rate.

The catalysts according to the present invention also act effectively asan oxidization catalyst for hydrocarbon (HC) and carbon monoxide (CO) ifan oxidization atmosphere is available.

g TEST EXAMPLE 2 TEST EXAMPLE 3 The test was made under the followingconditions by This test proves that the catalysts according to thisusing the same analyzing devices as in. Test Example 1. invention areeffective for purifying harmful NO com- 5 ponents contained in internalcombustion engine exhaust gas.

The catalyst was made by machining this 'systems (1) Test alloy withvarious components, as given in Table 7, to

CO measuring meter was used.

Test gas: CQ produce cuttings by forming an oxidized layer, by reg ggggPP"! ducing, and then stuffing into the catalyst converter for N: therest ,I purifying internal combustion engine exhaust gas.

(1) Test conditions Internal combustion engine: 1900cc four cylinderreciprocal gasoline engine Installation location of Just behind theexhaust manifold catalyst converter: and approximately 40cm back fromthe cylinder head Shape of catalyst converter: Cylindrical type with70mm diameter and 300mm length. Capacity 1.2 lit. Type of catalyst:Catalysts with compositions given in Table 7. Stuffed compactly. Weight:Approx. 2.0kg Apparent surface area: Approx. 20000 cm Engine operation:Steady bench test operation Condition: A 2700 rpm 2.2kg rn B 2500 rpm1.2kg m Catalyst bed temperature: A 660C. B 630C. S.V.: A 40,000 V/V,.hr B 27,000 V/V,,. hr

Gas flow rate: 2.5 l/minute Measurement was made by an exhaust gasanalyzing Amount of catalyst: Sml meter Type of catalyst: Ni-24% Cucatal st in a bent sheet with 0 cm Results of pp surface area NO and COwere purified approximately 100% S.V.. 30,000 v/v,. hr r Catalyst bedtemperature: 300 700C, and l 1% respectively, as shown in Table 7. As aresult of testing with alloys other than this systems alloy, bothachieved a slight purification rate.

Table 7 Alloy component Engine N0 C0 operapurifipurifi- Specimen tingcation cation condirate rate No. Cu Ni Fe Others tion 35- 9.4 45.0 bal A58.3 10.7 B 98.0 5.0 36 9.0 43.3 bal Cr- 3.7 A 55.5 9.9 B 94.4 4.6 379.2 39.5 bal Co- 1.3 A 40.5 8.3 B 89.9 4.7 38 8.9 41.7 bal Co-I5.7 A49.7 9.1 B 92.3 5.0 39 8.8 42.6 bal Co- 5.3 A 45.2 8.9

Cr- 4.1 Ce- 2.5 B 88.3 4.4

Note:

Average exhaust gas composition under operating condition A N0-2400 ppmC0-2.2% l-lC-l 10 ppm Average exhaust gas composition under operatingcondition B NO-600 ppm C0-4.5% I-IC-l ppm 2. Results As seen from theevaluations based on the above test Both NO and CO were remarkablypurified from the examples, this systems alloy achieves an outstandinglow temperature side as illustrated in FIG. 2. The term effect asreduction oxidization catalysts. Also as proven Oxidization" given inFIG. 2 denotes that an oxidized by embodying examples and test examples,the alloy is layer formed by treating in atmosphere at 900C. for 12obtainable at low cost due to extensive selection range hours waspresent and the term Reduction after oxidiof alloys. Moreover, the alloyis a highly strong and zatlon denotes that it was subsequently subjectedto excellent in plasticity, workability and castability as hydrogen gasreduction at 800C. for 2 hours. well as heat resistance and corrosionresistance. Therefore, it can advantageously be formed into cuttings,sheets, pipes, etc. according to application.

What is claimed is:

1. An exhaust gas purifying catalyst comprising an alloy consistingessentially of 01-40% Cu and the balance of at least one of the groupconsisting of Ni, Fe, and a combination of Ni and Fe by weight asfundamental components, and including a surface formed by firstoxidizing the alloy by heating at 700C. 1100C. in an oxidizingatmosphere for k to 24 hours to provide an oxidized layer at least p. inthickness, and thereafter reducing the oxidized layer in a reducingatmosphere at approximately 800C. for about 2 hours.

sired containing 0.1 40% of Cu and the balance of at least one of Ni andFe as fundamental components and forming an oxidized layer of more thanlOp. in thickness on the surface of said shaped alloy by heating same at800- l300C. in an oxidization atmosphere for 3 24 hours, and thereafterreducing the oxidizing layer by heating same in a reducing atmosphere atapproximately 800C. for about 2 hours.

1. AN EXHAUST GAS PURIFYING CATALYST COMPRISING AN ALLOY CONSISTINGESSENTIALLY OF 0.1-40% CU AND THE BALANCE OF AT LEAST ONE OF THE GROUPCONSISTING OF NI, FE, AND A COMBINATION OF NI AND FE BY WEIGHT ASFUNDAMENTAL COMPONENTS, AND INCLUDING A SURFACE FORMED BY FIRSTOXIDIZING THE ALLOY BY HEATING AT 700*C.-1100*C. IN AN OXIDIZINGATMOSPHERE FOR 1/2 TO 24 HOURS TO PROVIDE AN OXIDIZED LAYER AT LEAST 10$IN A THICKNESS, AND THEREAFTER REDUCING THE OXIDIZED LAYER IN A REDUCINGTAMOSPHERE AT APPROXIMATELY 800*C. FOR ABOUT 2 HOURS.
 2. An exhaust gaspurifying catalyst according to claim 1 including 40% or less of atleast one of the group consisting of Co and Cr.
 3. A process ofproducing a catalyst for purifying exhaust gas which comprises shapingan alloy as desired containing 0.1 - 40% of Cu and the balance of atleast one of Ni and Fe as fundamental components and forming an oxidizedlayer of more than 10 Mu in thickness on the surface of said shapedalloy by heating same at 800*- 1300*C. in an oxidization atmosphere for3 - 24 hours, and thereafter reducing the oxidizing layer by heatingsame in a reducing atmosphere at approximately 800*C. for about 2 hours.